Styrenes hydroformylation

Scheme 9.3 Formation of Crudden s pre-catalysts for styrene hydroformylation...

The hydroformylation of styrene using rhodium systems containing the four structurally related diphosphines dppe, dppp, (86), and (87) has been studied. A systematic analysis of the effect of the pressure, temperature, and the ligand metal molar ratio shows that the five- and six-membered ring chelating diphosphines behave differently from one another.347 An analysis of the effect of pressure, temperature, and ligand metal molar ratio on the selectivity of styrene hydroformylation catalyzed... 

Rh(acac)(CO)2] in combination with ESPHOS (76a) was applied in the asymmetric hydroformylation of vinyl acetate with excellent results. ESPHOS was effective in styrene hydroformylation, but the product is essentially racemic.270... 

The monosulfonated PPh derivative, Ph2P(m-C6H4S03K) (DPM) and its rhodium complex, HRh(CO)(DPM)3 have been synthesized and characterized by IR and NMR spectroscopic techniques. The data showed that the structure was similar to [HRh(CO)(PPh3)3]. The catalytic activity and selectivity of [HRh(CO)(DPM)3] in styrene hydroformylation were studied in biphasic catalytic systems.420 421 Rh1 complexes [Rh(acac)(CO)(PR3)] with tpa (131), cyep (132), (126), ompp (133), pmpp (134), tmpp (135), PPh2(pyl), PPh(pyl)2, and P(pyl)3 were characterized with NMR and IR spectra. Complexes with (131), (132), and (126) were catalysts for hydrogenation of C—C and C—O bonds, isomerization of alkenes, and hydroformylation of alkenes.422 Asymmetric hydroformylation of styrene was performed using as catalyst precursor [Rh(//-0 Me)(COD)]2 associated with sodium salts of m-sulfonated diarylphosphines.423... 

Optical yields up to 17% and 25%, respectively, have been reached in the styrene hydroformylation in the presence of cobalt or rhodium catalysts using N-alkylsalicylaldimine or phosphines as asymmetric ligands. Furthermore the hydroformylation of aliphatic and internal olefins have been achieved using rhodium catalysts in the presence of optically active phosphines. With the same catalysts, cis-butene surprisingly undergoes asymmetric hydroformulation with optical yields up to 27%. On the basis of the results obtained for cis-butene and the asymmetric induction phenomena in dichlor(olefin)(amine)platinum( 11) com-... 

Styrene hydroformylation with [(-)-BPPM]PtCl2 and added SnCh to yield a mixture of 2- and 3-phe-nylpropanal has been carried out in benzene at different reaction pressures (100-180 bar), temperatures (50-95 °C) and reaction times (2-15 h equation 34).39 The normal to branched ratio was relatively high... 

Table 6. Face of the unsaturated prochiral carbon atom preferably attacked by CO in 1-butene and styrene hydroformylation...

Leitner reported that lower densities of SCCO2 can be used to extract product from a reaction mixture without coextraction of a homogeneous catalyst. This process, which he called CESS (catalysis and extraction using supercritical solution), was demonstrated with styrene hydroformylation [Eq. (23), ligand L ] and imine hydrogenation [Eq. (22)]. The catalyst was used for three cycles before drops in the conversion and selectivity was observed (101,111,133). Sellin and Cole-Hamilton used catalysts specifically chosen for their insolubility in SCCO2 to facilitate the catalyst/product separation in a CESS process (134). 

Suppression of aldehyde product racemization under the reaction conditions can be achieved with ethyl orthoformate21-45, l34,158. Thus, nearly quantitative induction is observed when a BPPM-modified platinum catalyst is used for styrene hydroformylation in the presence of orthoformate as the trapping agent for the chiral aldehyde formed125-, 58. These results, however, are reported to be not reproducible48, S3-177. 

Zeise s salt, modified with chiral aminophosphane-phosphinites (AMPP), can also be used as a catalyst precursor in asymmetric styrene hydroformylation113. Other catalytic platinum systems for the hydroformylation of styrene are platinum(O)- alkene complexes of the type [Pt(C2H4)(L2)] L2 = l,2-bis[(diphenylphosphino)methyl]benzene and ( + )-Diop 24. When activated with methanesulfonic acid, catalysts for styrene hydroformylation are formed, which give total yields of aldehydes ranging from 44 to 67% and selectivities towards linear 3-phenyl-propanal ranging from 80 to 88%. Smaller amounts of the corresponding alcohols (3-18%) are also obtained with a pronounced selectivity towards 3-phenylpropanol of 94-96%. However, when Diop complexes of this type are used, no asymmetric induction in hydroformylation can be detected24. 

Molecular Imprinting and Sol-Gel Encapsulated Rh Catalysts for Styrene Hydroformylation... 

The effects of bisphosphite ligand structure on regioselectivity and enantio-selectivity in asymmetric styrene hydroformylation are shown in Table 1. Catalytic reactions were preformed at ambient temperature and 130 psi CO/H2. Hydroformylation regioselectivity was determined by GC of the product aldehydes. Enantioselectivity was determined by chiral GC after conversion to the carboxylic acid (eqn 1). The, i -enantiomer of the bisphosphites in Figure 1 all produced the... 

Table 1 Structure-property relationships for styrene hydroformylation. Condi-... 

This observation demonstrates that the catalyst resting state under hydroformyla-tion conditions is Rh(l)(CO)2H. In addition, these in situ infrared studies demonstrated that styrene hydroformylation using bisphosphite 1 is first order in both styrene and Rh concentrations. 

Effective control of chemo and steric selectivity of a chemical reaction lies in our ability to manipulate nano-environment of active sites. Due to difiGculty in manipulating the active site on the nanoscale and lack of fxmdamental nderstanding of the reaction mechanism, development of chemo- and stereoselective catalysts has relied heavily upon empirical studies. One successful xample of fine-tuning steric environment of the active site is the use of chiral diphosphite ligands to control the selectivity of styrene hydroformylation on Rh omplex catalysts (1-3). 

Hydroformylation reaction. Styrene hydroformylation was carried out in an in situ high pressure infrared (IR) cell at a total pressure of 0.83 MPa. 0.1 g catalyst was pressed into a self-support disk and placed inside the IR cell. The reactor was heated up to the desired temperature and 0.2 ml styrene was injected slowly into the cell in the CO and H2 flow [CO/H2 (v/v) =1/1, total flow rate = 30 ml/min] to give a reactants molar ratio of CO H2 styrene = 1 1 1148. The reactor was pressurized to 0.83 MPa and the reaction was carried out in a batch mode. The IR spectra were collected during the entire course of reaction studies by a Nicolet MAGNA 550 Series II Fourier transform infrared spectrometer... 

The surface of 1.9 wt% Rh/sol-gel and 4.5 wt% Rh/polymer catalysts were characterized by CO adsorption. Figure 1 shows the IR spectmm of CO adsorption at 0.1 MPa and 298 K as well as the styrene hydroformylation temperature program reaction (TPR) over the Rh/sol-gel catalyst. Adsorption of CO on the catalyst produced a gem-carbonyl band at 2086 and 2015 cm", indicating that highly dispersed oxide rhodium sites were formed on the catalyst surface. Styrene was brought to contact with adsorbed CO on the catalyst surface by CO and H2 flow. 

Figure 2 shows the in situ IR spectra of styrene hydroformylation over 1.9 wt% Rh/sol-gel catalyst at 373 K and 0.83 MPa. Phenylpropanals, indicated by the C=0 stretching vibration at 1717 cm-i, formed after 2 min of the reaction in the batch mode. The IR intensity of the C=0 band increased with the reaction time. The sol-gel encapsulated Rh catalyst exhibited high stability at all reaction conditions. No rhodium leakage has been observed for the entire reaction process. However, a higher loading Rh/sol-gel catalyst is difficult to obtain by the sol-gel encapsulation approach due to the limited solubility of the Aliquat 336, [(CgHivlaN eJCf, which is needed to pair with RhCb- 3H 0. 

Figure 3 shows the IR spectrum of CO adsorption at 0.1 MPa and 298 K as well as the styrene hydroformylation over 4.5wt% Rh 2-phenylpropanal-imprinted catalysts at 353 K and 0.83 MPa. Observation of gem-dicarbonyl at 2086 and 2015 cm-i upon CO adsorption indicated that Rh sites are in the highly dispersed state. 2-phenylpropanal and 3-phenylpropanal were formed after 1 min of the reaction in the batch model as shown by the appearance of the phenylpropanals carbonyl band at 1717 cm-i. The IR intensity of phenylpropanals increased with the reaction time. Table 2 summarizes the conversion, selectivity, and turnover frequency (TOF) of hydroformylation over... 

Lin, B. Akgerman, A. Styrene Hydroformylation in Supercritical Carbon Dioxide Rate and Selectivity Control. Ind. Eng. Chem. Res., 2001, 40, 1113-1118... 

Water-soluble metal complexes of rhodium with polyamidoamine-based (PAMAM-based) third-generation (32 terminal groups) dendrimers modified with diphenylphosphine groups have been used in two-phase hydroformylation of 1-octene and styrene. The selectivity in styrene hydroformylation with respect to isoaldehyde was much higher than in the case of trisulfonated triphenylphosphine... 

Loeber [223] S3mthesized a complex 82, which was tested in styrene hydroformylation. Theoretically predicted conversion of the initial compound took place in 48 h at a pressure of 4.0 MPa at a high (95%) selectivity with respect to phenylpropanal. A catalytic system consisting of [Rh(nbd)Cl]2 and phosphine was more active. 

Chiral diphosphines such as 17,18, and 19 as modificators in platinum-tin systems were found to lead to high enantiomeric excesses (80-96%) in styrene hydroformylation, but the chemo- and regioselectivity is generally low (121 122)... 

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